Electronic equipment always generates heat, largely as a consequence of the fact that no electronic system is one hundred percent efficient. Some of the input power of the system must, of necessity, be dissipated as heat.
With the advent of the semiconductor, it became possible to construct electronic systems that operate at low power consumption. These early solid-state electronic systems generally exhibited low overall power consumption, and, consequently, even at low efficiency, there was little heat. Only applications requiring high power to be generated somewhere within the equipment, such as radio transmitter implementations, had hot spots within the equipment requiring the use of heat sinks and/or cooling fans.
Early computers were virtually room-size because of the need for massive numbers of switching circuits that could only be provided through the use of vacuum tubes. Since vacuum tubes were inherently inefficient, much of the size and expense of early computer systems is attributable to power supplies and cooling systems. As the transistor, and eventually the integrated circuit, became more ubiquitous, the size and power requirements of computer systems decreased dramatically.
Because microprocessor systems are so small and use so little power, availability of portable, battery-powered systems has grown by leaps and bounds. But many new application programs require large amounts of processing power, and high-speed operation of new, sub-micron geometries requires the expenditure of considerable amounts of power.
This has not discouraged the development of faster processors or portable systems, however. Fixed equipment that is not dependent upon batteries for power can tolerate the additional power consumption that cooling fans require, and, because of the recent development of batteries with very high capacities, even in small packages, portable computing equipment can take advantage of new, more powerful processing technologies by conceding the need for cooling fans and budgeting power accordingly.
Of course, even the best of the modern battery packs do not have unlimited power, and there are environmental standards associated with acoustic noise that is produced by fans running at high speed. In many forms of high performance equipment, such as high-speed, high-capacity file servers, multiple processors generate sufficient heat that banks of cooling fans, as many as eight or sixteen, for example, can be required to achieve acceptable cooling. Acoustic concerns make it desirable to run the fans at low speed in order to reduce the noise level, but it may be impossible to provide adequate cooling at low fan speeds, even though environmental requirements related to noise levels may best be met through low fan speed operation. It should not be necessary to compromise equipment cooling for the sake of compliance with noise-emission standards. After all, lack of proper cooling can shorten component life, and the cost of system maintenance continues to mount.
It has long been recognized that temperature-proportional speed control can be accomplished through the use of pulse width modulation (PWM). There are a number of devices known in the art that provide PWM fan speed control in response to a temperature signal from an external temperature sensor.
Even though the devices currently available are capable of providing fan speed control in response to a temperature signal, these devices do not permit operational parameters to be reprogrammed easily to accommodate the thermal peculiarities of a particular chassis, nor do they allow an external controller to supervise fan management without taking over fan operation completely. These devices universally fall short of providing an adequate interface to an external control element for maximum flexibility in a wide range of applications.